How to realize DTMF signal by two sin signals.

[billchen]

How to realize DTMF signal by two sin signals.
DTMF signal is combined by two sin signals(low frequency and high frequency).
Thanks to your any idear.

 

[throwaway18]

You add the two sinusoidal signals together.

 

[billchen]

to throwaway18


Yes, I know.
BUt i want to know How to add the two sinusoidal signals together.
Can you explain it to me or tell me where can i get the answer.

 

[throwaway18]

If you are doing this digitally you take the values of the two sinusoids at a paticular point in time, add the numbers together and send the result to your DAC.

If you have two seperate analog signals then it can be as simple as feeding both signals into one point through resistors.

 

[echo47]

Here's a MATLAB demo of DTMF generation and detection:
**broken link removed**

 

[billchen]

Thanks,echo47.
But is seemed to be useless.
I want to know how to realize two sin signals add together.

To throwaway18
I confused with that the low frequency output signal will infect high frequency signal, when the two sin signals add together by resistor.

 

[throwaway18]

If the ouput impedance of the sinusoid generators is low compared to the mix resistors leakage will be negligable.

If it is a problem you either use buffers before the resistors or use a summing amplifer circuit like this

http://www.ecircuitcenter.com/Circuits/opsum/opsum.htm

The point where the resistors are connected together is held at zero volts by the action of the opamp so there is very little leakage from one input to another.

 

[billchen]

Thanks for your throwaway18.
I see.

Added after 3 minutes:

Sorry, it should be:"thanks for your help,throwaway18".